1. Field of the Invention
This invention is concerned with organic reinforcing fillers and their preparation.
2. Description of the Prior Art
Various materials have been proposed and used as reinforcing fillers for rubber. Carbon blacks are the major reinforcing fillers in use and treated fine particle silicas are also used for non-black applications. There have been proposed emulsion prepared polymers (not anionic) based on styrene-divinylbenzene with other monomers and graft polymers prepared by O. W. Burke, Jr. and others. A variety of copolymers and terpolymers were prepared by Burke et al. and this work has been summarized in "Reinforcement of Elastomers." Interscience, 1965, edited by G. Kraus, pages 511-527. These polymeric fillers were prepared by conventional emulsion polymerization using free radical initiators. To achieve the optimum reinforcing properties with fillers prepared in this manner it was necessary to polymerize the styrene divinylbenzene with additional monomers and to carry out additional grafting reactions on the formed particles. These polymerization methods require expensive monomers and lengthy polymerization times making the process uneconomic for the preparation of low cost fillers competitive with carbon black. Also to achieve optimum properties the secondary grafting reactions required further add to the cost of preparing filler materials. The best of these materials were deficient in properties in tire formulations, as compared with carbon blacks.